In a fiber laser device, pumping light is input to an amplifying optical fiber with a core doped with rare-earth elements and coated with a clad, and laser light such as signal light is amplified by the pumping light. Further, the amplified laser light is output from a core at one end of the amplifying optical fiber.
Such a fiber laser device has an optical combiner in some cases to input pumping light to the amplifying optical fiber. Patent Document 1 mentioned below discloses an example of the optical combiner.
In the optical combiner disclosed in Patent Document 1 below, a fiber for propagation of laser light which allows propagation of laser light such as signal light, and fibers for propagation of pumping light which allow propagation of pumping light are fused to a double clad fiber having a core and a clad. More specifically, an end of the fiber for propagation of laser light which allows propagation of laser light such as signal light and the end of the fibers for propagation of pumping light which allow propagation of pumping light are bundled, and the side surface of the fiber for propagation of laser light and the side surface of the fibers for propagation of pumping light are fused to each other. Further, the positions of the core of the fiber for propagation of laser light and the core of the double clad fiber having the core and the clad are aligned, and the end surface of the fiber for propagation of laser light and the end surface of the fibers for propagation of pumping light are fused to the end surface of the double clad fiber. Thus, laser light propagates between the core of the double clad fiber and the core of the fiber for propagation of laser light, and pumping light propagates between clads of the fibers for propagation of pumping light and the double clad fiber (Patent Document 1).